1. Field of the Invention
The present invention relates to a small geared motor mounted in a precision apparatus, such as an amusement apparatus, an audio-visual apparatus, a medical apparatus, or a camera.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2012-62963 discloses a technology in this field. This document describes a reduction gear mechanism including a clutch that stops transmitting power between an output shaft and a gear member in case of overload. In this reduction gear mechanism, the gear member includes a shaft-receiving portion in which the output shaft is rotatably inserted and an outer cylindrical portion that surrounds the shaft-receiving portion. A coil spring is disposed between the shaft-receiving portion and the outer cylindrical portion. The coil spring urges the shaft-receiving portion in a radially inward direction. The reduction gear mechanism includes a torque limiter which utilizes a frictional force applied between an inner peripheral surface of the shaft-receiving portion and an outer peripheral surface of the output shaft to transmit or stop transmitting power between the gear member and the output shaft.
However, with the above-described torque limiter, if the output shaft is locked for any cause, the gear member continuously rotates with respect to the output shaft while the frictional force is applied between the inner peripheral surface of the shaft-receiving portion and the outer peripheral surface of the output shaft in the circumferential direction. Accordingly, the outer peripheral surface of the output shaft and the inner peripheral surface of the shaft-receiving portion are gradually worn, and the output shaft easily slips along the gear member. As a result, stability of rotation of the output shaft with respect to the gear member is gradually reduced, and there is a risk that the rotating force cannot be reliably transmitted from the gear member to the output shaft.